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authorChristian Brauner <christian.brauner@ubuntu.com>2017-10-08 14:10:46 +0200
committerChristian Brauner <christian.brauner@ubuntu.com>2017-10-08 17:47:58 +0200
commit645ac9aaf89e3311949828546df6334322f48933 (patch)
treec3fcdd65127627d5f889060c145f238d953e2b1f
parent98e0742024d4c13c08a6076b3d119c250e7d0118 (diff)
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openpty: use TIOCGPTPEER to open slave side fd
Newer kernels expose the ioctl TIOCGPTPEER [1] call to userspace which allows to safely allocate a file descriptor for a pty slave based solely on the master file descriptor. This allows us to avoid path-based operations and makes this function a lot safer in the face of devpts mounts in different mount namespaces. [1]: https://patchwork.kernel.org/patch/9760743/ Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
-rw-r--r--ChangeLog3
-rw-r--r--login/openpty.c30
2 files changed, 27 insertions, 6 deletions
diff --git a/ChangeLog b/ChangeLog
index e1e98ad..da396ff 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,9 @@
* login/openpty.c (openpty): Close slave pty file descriptor on error.
+ * login/openpty.c (openpty): If defined, use the TIOCGPTPEER ioctl()
+ call to allocate the slave pty file descriptor.
+
2017-10-06 Joseph Myers <joseph@codesourcery.com>
* sysdeps/ieee754/ldbl-128/s_fma.c: Include <libm-alias-double.h>.
diff --git a/login/openpty.c b/login/openpty.c
index 9e556c2..6703128 100644
--- a/login/openpty.c
+++ b/login/openpty.c
@@ -94,6 +94,8 @@ openpty (int *amaster, int *aslave, char *name,
char *buf = _buf;
int master, ret = -1, slave = -1;
+ *buf = '\0';
+
master = getpt ();
if (master == -1)
return -1;
@@ -104,12 +106,22 @@ openpty (int *amaster, int *aslave, char *name,
if (unlockpt (master))
goto on_error;
- if (pts_name (master, &buf, sizeof (_buf)))
- goto on_error;
-
- slave = open (buf, O_RDWR | O_NOCTTY);
+#ifdef TIOCGPTPEER
+ /* Try to allocate slave fd solely based on master fd first. */
+ slave = ioctl (master, TIOCGPTPEER, O_RDWR | O_NOCTTY);
+#endif
if (slave == -1)
- goto on_error;
+ {
+ /* Fallback to path-based slave fd allocation in case kernel doesn't
+ * support TIOCGPTPEER.
+ */
+ if (pts_name (master, &buf, sizeof (_buf)))
+ goto on_error;
+
+ slave = open (buf, O_RDWR | O_NOCTTY);
+ if (slave == -1)
+ goto on_error;
+ }
/* XXX Should we ignore errors here? */
if (termp)
@@ -122,7 +134,13 @@ openpty (int *amaster, int *aslave, char *name,
*amaster = master;
*aslave = slave;
if (name != NULL)
- strcpy (name, buf);
+ {
+ if (*buf == '\0')
+ if (pts_name (master, &buf, sizeof (_buf)))
+ goto on_error;
+
+ strcpy (name, buf);
+ }
ret = 0;